Miniature tapped adjustable inductor



May 24, 1966 w. D. TIPPETT MINIATURE TAPPED ADJUSTABLE INDUCTOR FiledApril 14, 1964 LF/G. 2

INVENTOR W, D. TIPPETT BY I v v A TTORNE V United States Patent3,253,241 MINIATURE TAPPED ADJUSTABLE INDUCTOR William D. Tippett,Winston-Salem, N.C., assignor to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York Filed Apr. 14,1964, Ser. No. 359,797 Claims. (Cl. 336-15) This invention relate toinductive devices and to methods for making the same. More particularly,the invention relates to miniature inductive devices and to means andmethods for adjusting their electrical characteristics.

The invention is specifically directed to miniature tapped inductivedevices having adjustable windings for providing assigned inductancevalues. These devices may be used in various types of electricalequipment as, for example, in an electromagnetic delay line having aconsiderable number of these inductive devices arranged in an array withsuch close spacing as to be virtually touching each other. The design ofsuch a delay line ordinarily involves strict electrical requirementswhich generally necessitate precise adjustments of the inductance valuesabout the taps of the inductive devices and also accurate adjustments ofthe coeflicient of coupling between the windings of each of the devices.These adjustments are usually diflicult to accomplish because the tinysize of these inductive devices and the minute gauge of the fragile wireused in their windings render the making of adjustments a delicate andprotracted procedure.

Accordingly, an object of this invention is to provide an improvedminiature inductive device having a tap at an intermediate position.

Another object of the invention is to provide an improved method ofmaking a tapped inductive device having adjustable inductance values onopposite sides of the tap.

An additional object of the invention is to provide an improved methodfor quickly and precisely adjusting the electrical characteristics of aninductive device.

A further object of the invention is to provide improved means forvarying the windings of a tapped inductive device.

These and other objects of the invention are attained by employing adouble bobbin as the core of an inductive device and by providing thebobbin with a slotted flange at each end and a larger slotted flange atan intermediate point, such as at its center. Two windings are formed onthe bobbin with each winding being located between the central flangeand a respectively different one of the end flanges. Each winding has alead extending up through the slot in the middle flange for forming anintermediate tap. In addition, each winding has another lead extendinginto the slot in its respectively associated end flange. These'windingsare individually enclosed by cylindrical sleeves. Each sleeve isrotatably mounted on a respectively different one of the end flanges andabuts against a respectively different side of the middle flange. A slotis formed in the outer end of each sleeve for receiving the lead fromthe slot in its associated end flange. Thus, rotation of any one of thesleeves will carry the respectively received lead with it therebyforcing the lead to be wound upon the core when the sleeve is rotated inone direction, and to be unwound from the core when the sleeve isrotated in the opposite direction. In other words, the rotation of anyone of the sleeves will change the length of its associated windingthereby producing a corresponding change in the electricalcharacteristics of the inductive device.

These and other features of the invention are more fully discussed inconnection with the following detailed description of the drawing, inwhich:

FIG. 1 is a perspective view of one exemplary embodiment of an improvedinductive device constructed in accordance with this invention, and

FIG. 2 is an exploded perspective view, partly in section, of the sameinductive device.

The illustrative embodiment of the invention shown in FIG. 1 isrepresented as a substantially cylindrical center-tapped inductivedevice 1 which is approximately 0.180 inch in height and 0.200 inch indiameter. It is to be understood that, if desired, the tap may belocated at a different intermediate point other than the precise center.The inductive device 1 is provided with a double bobbin core 2 made ofsuitable magnetic material and formed with two end flanges 3 and 4 and alarger intermediate or central flange '5. Each of the flanges 3, 4, and5, which are integral with the core 2 has means defining slots therein,as is represented by the reference numerals 6, 7, and 8, for receivingor accommodating winding leads. The inductive device 1 further comprisestwo windings or coils 9 and 10 with the upper winding 9 being wound onthat portion of the double bobbin core 2 that extends between theintermediate or central flange 5 and the upper end flange 3, while thelower winding 10 is formed on the bobbin part of the core 2 which liesbetween the middle flange 5 and the lower end flange 4.

The windings 9 and 10 are individually enclosed by means of cylindricalsleeves 11 and 12 which are each rotatably mounted on a respectivelydifferent one of the end flanges 3 and 4 while abutting againstrespectively different sides of the intermediate or middle flange 5. Asis indicated in FIG. 1, the sleeves 11 and 12 have means defining slots13 and 14 in their outer ends through which protrude leads 15 and 16which are brought up from the windings 9 and 10, respectively, throughthe slots 6 and 8 as is more fully explained hereinafter. Each of thewindings 9 and 10 has another lead which extends out through one of theslots 7 in the middle flange 5. These last-mentioned leads are joinedtogether for the purpose of forming an intermediate or center tap 17.Thus, the inductive device 1 can be connected to any suitable electricalcircuit or equipment by means of the middle tap 17 and the leads 15 and16.

The electrical characteristics, particularly the inductance values, ofthe inductive device 1 can be adjusted or varied by manually rotatingone or both of the sleeves 11 and 12 in either a clockwise orcounterclockwise direction. When one of the sleeves 11 or 12 is rotatedin one direction, it will carry with it the associated lead '15. or 16which will be wound upon the core 2 thereby increasing the length of therespectively associated wind-.

ing 9 or 10. Conversely, rotation of the sleeve 11 or 12 in the oppositedirection will carry with it the associated lead 15 or 16 which will nowbecome unwound from the core 2 thereby decreasing the length of theassociated winding 9 or 10. These changes in the length of the wire ineither or both of the windings 9 and 10 produce corresponding changes inthe overall electrical characteristics, or inductance values, of theinductive device 1. Due to this novel construction, extremely preciseadjustments of the inductance 1 can be quickly accomplished throughproper rotation of the sleeves 11 and 12.

In the manufacture of the inductive device 1, the flanged double bobbincore 2 and the sleeves 11 and 12 are fabricated from a suitable powderedmagnetic material, such as carbonyl TH. The material for the core 2 andthe sleeves 11 and 12 may be supplied in the form of molded slugs havingthe appropriate diameters and lengths. If desired, the material may besupplied in the form of molded rod stock having the required outsidediameter, such as 0.200 inch. In this latter case, a section having theappropriate length or height for the core 2, such as 0.180 inch, wouldbe cut off from the rod stock and then formed, such as by a suitablegrinding process, into the desired double bobbin shape. The sleeves 11and 12 could also be cut from the same rod stock and have their centralbores formed by drilling.

The central flange and the sleeves 11 and 12 retain the diameter of therod stock, but the end flanges 3 and 4 are reduced by grinding so thattheir outside diameter is about 0.002 inch less than the inside diameterof the sleeves 11 and 12. This enables the sleeves 11 and 12 to fitsnugly over the end flanges 3 and 4 with minimal air gaps. Each sleevehas a length equal to the distance from the outside face of itsrespectively associated end flange 3 or 4 to the nearest side of themiddle flange 5 as is represented in FIG. 1. Thus, when the sleeves 11and 12 are mounted on the end flanges 3 and 4, the inductive device 1will be substantially cylindrical in shape.

Before the sleeves 11 and 12 are placed on the end flanges 3 and 4, anumber of slots are cut in the various parts by any suitable method,such as by grinding. These slots, which may conveniently all be of thesame width, include a pair of slots 7 in the central flange 5, a pair ofslots 6 in the upper end flange 3, a pair of slots 8 in the lower endflange 4, a slot 13 in the upper sleeve 11, and a slot 14 in the lowersleeve 12. The slots comprising each of the pairs 6, 7, and 8 are formed180 degrees apart, as is illustrated in FIG. 2, and extend downwardthrough their respective flanges 3, 4, and 5 until they approach thesurface of the core 2. As can also be seen in FIG. 2, each of thesleeves 11 and 12 has only one slot 13 and 14, respectively. The depthof each of the slots 13 and 14 is about 0.013 inch greater than thewidth of the respectively associated flanges 13 and 14 in order toprovide space for accommodating the end leads 15 and 16 as is shown inFIG. 1.

After the double bobbin core 2 has been fabricated, the two windings orcoils 9 and are formed on the double bobbin core 2 with each of thewindings 9 and 10 being located between the central flange 5 and arespectively different one of the end flanges 3 and 4. These windings 9and 10 may preferably be made from a single length of wire, such as 40gauge wire, which is bent in the middle and doubled back upon itself bytwisting for a length of about an inch, as is represented in thedrawing, for the purpose of forming the center tap 17. The insulation onthislooped section of wire is removed and the section is solder-tinnedso as to make one solid lead or tap 17.

The center tap 17 is placed in one of the slots 7 in the central flange5. This slot 7 accommodates the tap 17 with the end of the tap 17protruding outwardly therefrom, as is best seen in FIG. 2. The oppositelengths of wire are then wound around the core 2 in a series-aidingmanner. The winding operation proceeds from the central flange 5outwardly around the core 2 toward the respective end flanges 3 and 4until the desired lengths of the windings 9 and 10 have been formed.Thus, the

flange 5 constitutes spacing means at an intermediate point on the core2 for separating the windings 9 and 10 into two coils, and also providesmeans for accommodating or receiving the center tap 17. The windings 9and 10 are held in place On the core 2 by wrapping small pieces of asuitable tape around them. The ends of the wire are then brought outthrough the nearest ones of the respectively associated end slots 6 and8 to form the end leads 15 and 16.

These end leads 15 and 16 are fed through the bores in the sleeves 11and 12 which are then mounted upon their respectively associated endflanges 3 and 4. The sleeves 11 and 12 are pushed inward so as to abutagainst the sides of the central flange 5 thereby minimizing the airgaps between the sleeves 11 and 12 and the central flange 5. The sleeves11 and 12 are temporarily held in these positions by means of smallpieces of suitable tape. It should be noted that each of the sleeves 11and 12 is so oriented that its respective slot 13 or 14 faces outward asis shown in the drawing.

The inductive device 1 is now connected to a suitable inductancemeasuring device, such as an inductance bridge, and its total inductancevalue is measured. The inductance value of the winding 9 in the uppersection of the device 1 and the inductance value of the Winding 10 inthe lower section of the device 1 are separately measured. From thesemeasurements, the coeflicient of coupling can be readily calculated in amanner known to those skilled :in the art.

If these measurements indicate that the inductance value of either theupper or lower section of the device 1 is too low or too high, thenecessary corrective adjustments can be quickly and preciselyaccomplished by the following method. For example; let it be assumedthat the inductance value for the upper section 9 is too low. The firststep in the method of adjustment is to loosen the tape holding the uppersleeve 11 and then to rotate the sleeve 11 on the associated end flange3 so as to align the sleeve slot 13 with that one of the diametricallyopposed flange slots 6 which holds the upper end lead 15. The next stepis to pull the end lead 15 upwardly Out of the flange slot 6 and intothe sleeve slot 13 so as to protrude therefrom. The sleeve 11 is thenrotated in a positive direction with respect to the direction of theturns comprising the winding 9. During this rotation, the sleeve 11carries with it the lead 15 thereby forcing a portion of the lead 15 tobe Wound on the core 2. This. increases the total length of the winding9 and consequently increases its inductance value.

The sleeve 11 is secured in this new position by means of the tape, andthe inductance of the upper section 9 of the device 1 is again measured.If the inductance value is now too high, the sleeve 11 is rotated in anegative direction with respect to the direction of the turns of thewinding 9. This movement causes the sleeve 11 to carry with it the lead15 which is thus unwound from the core 2. Accordingly, the total lengthof the winding 9 is correspondingly reduced thereby producing areduction in its inductance value.

This process is duplicated by rotating the sleeve 12 around the windingsection 10 for adjusting its inductance value. Thus, by using thismethod, the lengths of the windings 9 and 10 can be adjusted to providethe desired inductance values. When this condition has been obtained,the sleeves 11 and 12 are again secured in place with small pieces oftape. If desired, the sleeves 11 and'12 can be permanently held in placeby means of a suitable cement, which may be inserted into their slots 13and 14, so that the finished product will be a fixed inductor.

In view of the above discussion, it can be understood that, through thismethod of adjustment, precise determination and adjustment of theinductance values about i In other words,

ship to each other and to the total series-aiding inductance of thedevice 1.

It should be noted that the design of the inductive device 1 furtherfacilitates other adjustments or changes in the coeflicient of coupling.Specifically, the slots 7 in the central flange 5 readily permitcross-over of the winding turns from one section 9 to the other section10 and vice versa. This enables different types of winding constructionto be made which thereby provide various choices of couplingcoeflicients between the windings 9 and 10.

Finally, it should be further noted that the magnetic shielding of thedevice 1, such as that provided by the abutment of the sleeves 11 and 12against the central flange 5, restricts the magnetic fields of thesections 9 and 10 to completely internal magnetic paths. This reducesthe external field of the inductive device 1 to a minimum with theresult that several of the devices 1 may be placed in an array with suchclose spacing as to be virtually touching each other, such as in an as-H sembly for an electromagnetic delay line, without producing anyobjectionable magnetic field interaction between them. 1

What is claimed is:

1. A shielded inductive device comprising a core of magnetic material,

a length of wire wound around said core for forming at least oneinductive winding thereon,

an end of said wire being disposed at one end of said core for formingat least one end lead to said wind- 111g,

shielding means for shielding said winding,

said shielding means including at least one sleeve of magnetic materialenclosing said winding,

and adjusting means for adjusting the length of said winding,

said adjusting means including means formed of magnetic material at saidend of said core for supporting said sleeve for rotation around saidshielded Winding,

and means for alternatively winding and unwinding said end lead withrespect to said core,

said last-mentioned means including means in said sleeve for receivingsaid end lead and for carrying it during said rotation of said sleeve.

2. A shielded inductive device comprising a core of magnetic material,

wire wound on said core for forming inductive windings thereon,

at least two ends of said wire being disposed at opposite ends of saidcore for forming end leads,

spacing means of magnetic material formed at an intermediate point onsaid core for separating said windings into two coils,

shielding means for shielding said coils,

said shielding means including at least two sleeves of magnetic materialeach enclosing a respectively different one of said coils,

and adjusting means for adjusting the lengths of said coils,

said adjusting means including means for supporting said sleeves forrotation around said enclosed coils,

and means for alternatively winding and unwinding said end leads withrespect to said core, I

said last-mentioned means including means in each of said sleeves forreceiving a respectively diflerent one of said end leads therein and forcarrying it during rotation of said sleeve.

3. A shielded inductive device comprising a core of magnetic material,

a single length of wire wound on said core for forming inductivewindings thereon,

the ends of said wire being disposed at opposite ends of said core forforming end leads to said windings,

means for forming an intermediate tap to said windlngs, A

accommodating means at an intermediate point on said core foraccommodating said intermediate tap,

and instrumentalities for varying the length of the windings on eachside of said tap,

said instrumentalities including two sleeves of magnetic material eachadapted for co'vering said windings on respectively diflerent sides ofsaid tap and for abutting against opposite sides of said accommodatingmeans, and means at each end of said core for rotatably supporting arespectively diiferent one of said sleeves,

each of said sleeves having means defining an opening therein foraccommodating the outward protrusion therefrom of the respectivelyassociated end lead,

and each of said last-mentioned means being adapted for forcing therespectively associated end lead to be wound upon said core in responseto the rotation of the respectively associated sleeve in one directionand for forcing said lead to be unwound from said core when said sleeveis rotated in the opposite direction.

4. A shielded inductive device comprising a core of magnetic material,

a single length of wire wound around said core for forming inductivewindings thereon,

the ends of said wire being disposed at opposite ends of said core forforming end leads to said windings,

said wire being looped at an intermediate point along its length forforming an intermediate tap to said windings,

a member formed of magnetic material on said core for accommodating theprotrusion of said intermediate tap therefrom,

shielding means for shielding said windings,

said shielding means including two sleeves of magnetic materialsurrounding the windings on said core with each sleeve being disposedbetween a respectively different end of said core and a respectivelydifferent side of said member,

and adjusting means for separately adjusting the length of each of saidwindings on opposite sides of said intermediate tap,

said adjusting means including means formed of magnetic material at eachend of said core for supporting said sleeves for individual rotationaround said windings,

each of said sleeves having means for receiving a re spectivelydifferent one of said end leads and for carrying said respectivelyassociated end lead with it during rotation of said sleeve whereby saidrespectively associated end lead is alternatively wound and unwound withrespect to said core.

5. An adjustable shielded inductive device comprising a double bobbin ofmagnetic material having a flange at each end and also at its center,

said center flange having a larger diameter than any one of said endflanges,

each of said three flanges having means defining a slot therein,

two windings on said bobbin each located between said center flange anda respectively different one of said end flanges,

each of said windings having a lead extending into the slot in therespectively associated end flange and another lead extending into theslot in said center flange and-protruding therefrom for forming a centertap,

and adjusting means for varying the inductance value of any one of saidwindings,

said adjusting means including two cylindrical sleeves of magneticmaterial each surrounding a respectively 7 a different one of saidwindings and each being ro- References Cited by the Examiner tatablymounted on a respectively difierent one of UNITED STATES PATENTS saidend flanges While abutting against a respectively 1,855,392 4/1932Gebhard 336137 different side of sand center flange, 1 930 714 10/19 3and each of said sleeves having means defining a slot 5 3 Hemtz. 336 137in its outer end for receiving therein the lead in 2929132 3/1960Wohlhleter 29 155'57 3,153,841 10/1964 Schrot 29155.57

the slot in the respectively associated end flange whereby rotation ofany one of said sleeves eifects ROBERT SCHAEFER Primary Examiner achange in the length of the respectively associated winding with acorresponding change in its induc- 10 JOHN BURNS Examinertance. C.TORRES, Assistant Examiner.

1. A SHIELDED INDUCTIVE DEVICE COMPRISING A CORE OF MAGNETIC MATERIAL, A LENGTH OF WIRE WOUND AROUND CORE FOR FORMING AT LEAST ONE INDUCTIVE DISPOSED AT ONE END OF SAID AND END OF SAID WIRE BEING DISPOSED AT ONE END OF SAID CORE FOR FORMING AT LEAST ONE END LEAD TO SAID WINDING, SHIELDING MEANS FOR SHIELDING SAID WINDING, SAID SHIELDING MEANS INCLUDING AT LEAST ONE SLEEVE OF MAGNETIC MATERIAL ENCLOSING SAID WINDING, AND ADJUSTING MEANS FOR ADJUSTING THE LENGTH OF SAID WINDING, SAID ADJUSTING MEANS INCLUDING MEANS FORMED OF MAGNETIC MATERIAL AT SAID END OF SAID CORE FOR SUPPORT- 